Most electrophotographic toners are prepared by a melt kneading process. In the melt kneading process, a resin, a colorant, an antistatic agent, etc. are melt-kneaded, pulverized, and then classified to obtain grains. Recently, color or high resolution copying machines and printers employing electrophotographic processes become more popular. Toners for these apparatus have been accordingly required to have high performances. Further, due to its growing requirement for high performance, the hardware such as copying machines and printers has been rapidly complicated and thus has required a large amount of power. Thus, the hardware has been required to minimize the fixing energy. Accordingly, for the part of the toner for use with these copying machines or printers, finer grains have been required for fixability at a low temperature and high resolution. However, when finely divided toner grains are prepared by the melt kneading process, the classification yield is particularly poor, increasing the production cost. Further, if a low-temperature fixable material is used, it causes toner fusion in the pulverizer, lowering the productivity.
A wet process is considered to be an efficient process for the preparation of finely divided toner grains in a high yield. Examples of such a wet process include a supspension polymerization process, an emulsion polymerization process, and a dispersion polymerization process. Many processes have heretofore been proposed.
However, toners obtained by such a wet process are still insufficient in toner properties such as pigment dispersibility, cleaning properties, environmental stability of chargeability and sharpness of grain size distribution, as compared with those obtained by the melt kneading process. In particular, due to its nonuniform pigment dispersion and nonuniform location of charging sites on the surface of the toner, the toner obtained by the wet process is disadvantageous in that its chargeability varies so that a blur around the image occurs, making it impossible to obtain a high resolution image. Further, the inferior toner chargeability and charge distribution have adverse influence on toner scattering in copying machines or printers employing electrophotographic process and on developer life. Moreover, the problem of disposal of waste liquid must be solved. Therefore, no wet process has been put into practical use.